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<title>Chapter 32. Boost.Ratio 2.1.0</title>
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<div class="chapter">
<div class="titlepage"><div>
<div><h2 class="title">
<a name="ratio"></a>Chapter 32. Boost.Ratio 2.1.0</h2></div>
<div><div class="author"><h3 class="author">
<span class="firstname">Howard</span> <span class="surname">Hinnant</span>
</h3></div></div>
<div><div class="author"><h3 class="author">
<span class="firstname">Beman</span> <span class="surname">Dawes</span>
</h3></div></div>
<div><div class="author"><h3 class="author">
<span class="firstname">Vicente J.</span> <span class="surname">Botet Escriba</span>
</h3></div></div>
<div><p class="copyright">Copyright © 2008 Howard Hinnant</p></div>
<div><p class="copyright">Copyright © 2006, 2008 Beman Dawes</p></div>
<div><p class="copyright">Copyright © 2009-2012 Vicente
      J. Botet Escriba</p></div>
<div><div class="legalnotice">
<a name="ratio.legal"></a><p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></div>
</div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl class="toc">
<dt><span class="section"><a href="ratio.html#ratio.overview">Overview</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="ratio.html#ratio.overview.motivation">Motivation</a></span></dt>
<dt><span class="section"><a href="ratio.html#ratio.overview.description">Description</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="ratio/users_guide.html">User's Guide</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="ratio/users_guide.html#ratio.users_guide.getting_started">Getting Started</a></span></dt>
<dt><span class="section"><a href="ratio/users_guide.html#ratio.users_guide.tutorial">Tutorial</a></span></dt>
<dt><span class="section"><a href="ratio/users_guide.html#ratio.users_guide.Examples">Example</a></span></dt>
<dt><span class="section"><a href="ratio/users_guide.html#ratio.users_guide.ext_references">External Resources</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="ratio/reference.html">Reference </a></span></dt>
<dd><dl>
<dt><span class="section"><a href="ratio/reference.html#ratio.reference.std">Standard C++11 Functionality</a></span></dt>
<dt><span class="section"><a href="ratio/reference.html#ratio.reference.io">Ratio I/O</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="ratio/appendices.html">Appendices</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.history">Appendix A: History</a></span></dt>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.rationale">Appendix B: Rationale</a></span></dt>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.implementation">Appendix C: Implementation
      Notes</a></span></dt>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.faq">Appendix D: FAQ</a></span></dt>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.acknowledgements">Appendix E: Acknowledgements</a></span></dt>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.tests">Appendix F: Tests</a></span></dt>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.tickets">Appendix G: Tickets</a></span></dt>
<dt><span class="section"><a href="ratio/appendices.html#ratio.appendices.todo">Appendix H: Future Plans</a></span></dt>
</dl></dd>
</dl>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="ratio.overview"></a><a class="link" href="ratio.html#ratio.overview" title="Overview">Overview</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="ratio.html#ratio.overview.motivation">Motivation</a></span></dt>
<dt><span class="section"><a href="ratio.html#ratio.overview.description">Description</a></span></dt>
</dl></div>
<h4>
<a name="ratio.overview.h0"></a>
      <span class="phrase"><a name="ratio.overview.how_to_use_this_documentation"></a></span><a class="link" href="ratio.html#ratio.overview.how_to_use_this_documentation">How
      to Use This Documentation</a>
    </h4>
<p>
      This documentation makes use of the following naming and formatting conventions.
    </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Code is in <code class="computeroutput"><span class="identifier">fixed</span> <span class="identifier">width</span>
          <span class="identifier">font</span></code> and is syntax-highlighted.
        </li>
<li class="listitem">
          Replaceable text that you will need to supply is in <em class="replaceable"><code>italics</code></em>.
        </li>
<li class="listitem">
          Free functions are rendered in the code font followed by <code class="computeroutput"><span class="special">()</span></code>, as in <code class="computeroutput"><span class="identifier">free_function</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          If a name refers to a class template, it is specified like this: <code class="computeroutput"><span class="identifier">class_template</span><span class="special">&lt;&gt;</span></code>;
          that is, it is in code font and its name is followed by <code class="computeroutput"><span class="special">&lt;&gt;</span></code>
          to indicate that it is a class template.
        </li>
<li class="listitem">
          If a name refers to a function-like macro, it is specified like this:
          <code class="computeroutput"><span class="identifier">MACRO</span><span class="special">()</span></code>;
          that is, it is uppercase in code font and its name is followed by <code class="computeroutput"><span class="special">()</span></code> to indicate that it is a function-like
          macro. Object-like macros appear without the trailing <code class="computeroutput"><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Names that refer to <span class="emphasis"><em>concepts</em></span> in the generic programming
          sense are specified in CamelCase.
        </li>
</ul></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
        In addition, notes such as this one specify non-essential information that
        provides additional background or rationale.
      </p></td></tr>
</table></div>
<p>
      Finally, you can mentally add the following to any code fragments in this document:
    </p>
<pre class="programlisting"><span class="comment">// Include all of Ratio files</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">ratio</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">;</span>
</pre>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="ratio.overview.motivation"></a><a class="link" href="ratio.html#ratio.overview.motivation" title="Motivation">Motivation</a>
</h3></div></div></div>
<p>
        <span class="bold"><strong>Boost.Ratio</strong></span> aimed to implement the compile
        time ratio facility in C++11, as proposed in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2661.htm" target="_top"><span class="bold"><strong>N2661 - A Foundation to Sleep On</strong></span></a>. That document
        provides background and motivation for key design decisions and is the source
        of a good deal of information in this documentation.
      </p>
<p>
        Since C++11 is now universally available, this library is only retained for
        backward compatibility, and starting with Boost 1.84, it's implemented in
        terms of the standard <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">ratio</span><span class="special">&gt;</span></code> header.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="ratio.overview.description"></a><a class="link" href="ratio.html#ratio.overview.description" title="Description">Description</a>
</h3></div></div></div>
<p>
        The <span class="bold"><strong>Boost.Ratio</strong></span> library provides:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            A class template, <a class="link" href="ratio/reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio&lt;&gt;"><code class="computeroutput"><span class="identifier">ratio</span></code></a>, for specifying compile
            time rational constants such as 1/3 of a nanosecond or the number of
            inches per meter. <a class="link" href="ratio/reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio&lt;&gt;"><code class="computeroutput"><span class="identifier">ratio</span></code></a> represents a compile time
            ratio of compile time constants with support for compile time arithmetic
            with overflow and division by zero protection.
          </li>
<li class="listitem">
            It provides a textual representation of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio</span><span class="special">&lt;</span><span class="identifier">N</span><span class="special">,</span> <span class="identifier">D</span><span class="special">&gt;</span></code> in the form of a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_string</span></code>
            which can be useful for I/O.
          </li>
</ul></div>
</div>
</div>
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